Date: Fri, 25 Sep 1998 10:45:24 -0300 (EST)
From: "Renato F. Cantao" <cantao AT ime DOT unicamp DOT br>
To: Shue-Cheng CHEN <scchen AT ohriki DOT t DOT u-tokyo DOT ac DOT jp>
cc: djgpp AT delorie DOT com
Subject: Re: A Problem with Template Class
In-Reply-To: <360B4190.1C2DD19F@ohriki.t.u-tokyo.ac.jp>
Message-ID: <Pine.SUN.3.96.980925103500.20384B-100000@athenas.ime.unicamp.br>
MIME-Version: 1.0
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Hi Mr. Chen!

	I guess I've already had the same problem in the past.
	I don't know exactly why, but templates are not compiled in an
usual way. It seems to me that every time you make a "templatization", I
mean, when you try

	SimpleArray<float>  saf;
	SimpleArray<int>    sai;
	SimpleArray<double> sad;

the compiler creates code for each "new" data type. It creates a code for
"SimpleArray<float>", "SimpleArray<int>" and so on ...

	That means that when you make a template file, it must be
included, not compiled! Compilation takes place when you declare an
object template. I would do, for instance (details ommited):

// FILE: simarra.h
 
...
template <class T>
class SimpleArray
{
public:
  SimpleArray( const int& );
...
};

In another file: simarra.hpp

// FILE: simarra.hpp

...
template <class T>
SimpleArray<T>::SimpleArray( const int& s_ ): ...do some stuff here
{
...
}

And finally ...

// FILE: main.cc

#include "simarra.hpp" <- ATENTION!!! I'm including the HPP!!!

main()
{
  SimpleArray<float> s;

  ... and so on!

  return 0;
}

OK???? Let me know if it works!

				Renato F. CANTAO
				State University at Campinas
				Campinas - Brazil

On 25 Sep 1998, Shue-Cheng CHEN wrote:

> Hi!
> 
> 	I made a main program "test.cc" as follows,
> 
> #include <iostream.h>
> #include "simarra.h"    // Header for SimpleArray<class T>
> 
> int main()
> {
>      SimpleArray<float> a;
>      for (int i=1; i<=6; i++) {
>           a[i] = i * 1.1;
>           cout << a[i] << "  ";
>      }
>      cout << endl;
>      return 0;
> }
> 
> It's strange that this main program only works when I placed all 
> implementations of the class SimpleArray<T> in the same test.cc.
> 
> When the implementations of the main program and the class were 
> separated in two different files, e.g., test.cc and SimArra.cc,
> in the linking stage, I always got the messages
> 
> 1.o: In function `main':
> 1.cc:1: undefined reference to `SimpleArray<float>::SimpleArray(void)'
> 1.cc:2: undefined reference to `SimpleArray<float>::SimpleArray(void)'
> 1.cc:6: undefined reference to `SimpleArray<float>::operator[](int)'
> 1.cc:7: undefined reference to `SimpleArray<float>::operator[](int)'
> 1.cc:11: undefined reference to `SimpleArray<float>::~SimpleArray(void)'
> 1.cc(.text+0xc9): undefined reference to
> `SimpleArray<float>::~SimpleArray(void)'
> 1.cc(.text+0xf3): undefined reference to
> `SimpleArray<float>::~SimpleArray(void)'
> 1.cc(.text+0x113): undefined reference to
> `SimpleArray<float>::~SimpleArray(void)'
> 
> Why did it become undefined?
> 
> Thank you in advance.
> 
> Shue-Cheng Chen
>